Today, it is becoming increasingly popular to provide steering systems that utilize two or more power units rather than a single power unit. Basically, especially in trucks and off-the-road vehicles, the increased size and weight and the increased size of tires, has dictated the need for increased power to allow comfortable steering of the vehicle.
Typically, two steering gears are employed, one adjacent each wheel of the vehicle to provide the increased steering capacity. The steering function is more efficiently carried out when the power is applied immediately adjacent to the wheels. The steering gear units may be smaller and more compact in order to fit within the crowded confines under the truck. The steering linkage, including the tie rod connecting the two sides of the steering mechanism, is under much less strain in a duel system since the full working force does not have to be translated across the vehicle.
In the past, when these dual systems have been installed on vehicles, it has been common practice to simply mount the units and connect the drag links to the crank of the steering units without further thought. A problem that apparently arises is one of improper synchronization or coordination between the two power units. Depending upon the particular geometry of the steering linkage, the system of the prior art is beset by various degrees of chattering or fighting between the units. In the past, when the problem of steering chatter is acute, no specific steps were known to correct the system to make the dual system feasible. The designers simply went back to a single system, abandoning the advantages afforded by a dual system. This problem more than any other single factor has probably contributed to dual systems not having been accepted to any greater than they have.
In any steering system, dual systems included, the designer has also in the past followed the general rule of determining the connection of the drag link to the crank of the steering unit, and then simply positioning the output pinion on the rack so that full throw of the piston may be obtained. As stated however, depending on the particular geometry of the steering linkage, this "rule of thumb" policy has met with various degrees of failure. In some cases, the steering chatter may be so weak as to be barely detectable. In others, the vehicle shakes violently under certain circumstances. In all cases, efficiency and safety of the system are seriously impaired.
The geometry of the steering systems on modern vehicles is very complex, particularly since the wheels turn different angles for proper tracking of the wheels as the vehicle goes around a corner. This has made the solving of the problem all the more difficult.
I have determined the cause of the problem as preemptive feedback of power from the slave unit to the master unit through the tie rod. Until now, the problem has defied solution short of completely redesigning the steering system. This is not only extremely expensive, but in some cases the space limitations of the vehicle make it impossible. The desirability of the basic advantages of a dual system is an extra incentive to find a solution.
The solution should be in the form of a simple change with respect to the steering units in order to avoid the undesirable redesigning of the steering linkage of the vehicle. With such a prerequisite, it is contemplated that the principles of the invention could be applied to any vehicle, thus saving the manufacturer the expense and trouble of redesigning the entire steering system. On existing vehicles, a simple adjustment should correct the problem of steering chatter.